There is known an internal combustion engine on a vehicle including a controller for control at engine startup to reduce the amount of noxious HC in exhaust air at starting of the cold engine. The controller for control at engine startup receives inputs, such as engine speed and coolant temperature, and controls the quantity of intake air and the ignition timing based on these factors.
In a conventional controller disclosed in JP Laid-Open No. H10-30480 for control at engine startup, an idle speed control valve is disposed in a bypass air passage bypassing a throttle valve. An air-increasing control valve for engine startup is disposed in an air-increasing bypass air passage for bypassing the throttle valve. The air-increasing control valve is opened to increase air at engine startup when the engine speed increases to a certain speed after startup operation. In synchronization with this opening operation of the air-increasing control valve at engine startup, feedback control of the idle speed control valve starts. Target engine speed is effectively set at a high speed to facilitate activation of a catalyst.
In another conventional controller disclosed in JP Laid-Open No. H05-321730 for control at internal combustion engine startup, an air quantity-regulating valve regulates the air in a bypass passage for bypassing a throttle valve. Prediction control is performed based on a duty ratio in view of an opening angle of the air quantity regulating valve to improve startability of the engine. The duty ratio is gradually corrected and decreased when actual engine speed is above the engine speed calculated by addition of the target speed and a predetermined speed. Feedback control is performed based on a feedback duty ratio when the actual engine speed increased once and then reduced below the engine speed calculated by addition of the target speed and the predetermined speed so as to prevent the actual engine speed from decreasing below the target speed.
Also in another conventional controller disclosed in JP Laid-Open No. H10-47039, for control at engine startup, if coolant temperature is within a predetermined temperature and if the duration time after the engine startup is shorter than a predetermined time, then it is determined that the catalyst is not activated and an ignition timing is controllable. If the engine speed is at or above a target speed, ignition timing is retarded to increase exhaust temperature. If the engine speed is below the target speed, the ignition timing is advanced toward normal ignition timing. By increasing the exhaust gas temperature, the catalyst is activated at an early stage in using standard fuel to stabilize the fuel combustion in using heavy fuel.
Moreover, in an ignition-timing controller disclosed in JP Laid-Open No. 2000-9010, more than one pair of ignition coils in parallel includes primary and secondary coils in magnetic connection to a power switching element and a driving circuit. Each ignition coil has a secondary side connected through high voltage diodes having a break down voltage higher than a required secondary current for isolation. Thereby, ignition timing of multi-ignition is controlled with precision.
In the conventional controller for control at engine startup, it is typical that the ignition timing is retarded so as to activate the catalyst early to reduce the amount of HC in the cold engine, and bypassed air is supplied so as to maintain the engine speed at the target speed.
However, it is recently required to provide a lean amount of fuel under exhaust gas regulations. Use of heavy fuel of lower volatility than regular fuel results in undesirable fuel combustion, slow response to the target engine speed, engine stall or hesitation.
Accordingly, the conventional controller for control at engine startup depends on the property of the fuel and cannot achieve stable control of the cold engine. Engine stall or hesitation may occur to the detriment of drivability. Also, the amount of HC is not decreased.
Moreover, in the conventional controller, for control at engine startup, the catalyst does not rise to a sufficient activation temperature by the conventional control. There is no choice but to increase the support of the catalyst itself to manage the exhaust purification capacity.